There is presently a need in the bioprocessing and pharmaceutical industries for an aseptic control valve that provides both the characterized flow performance of a control valve and the design features and performance requirements that the handling of sterile and biological flow streams requires.
The requirements for materials, configurations, cleanliness and performance of aseptic valves are provided in ASME Standard BPE-2005.
Typically, all control valves that provide characterized control do so by utilizing a metering function inherent to their individual design. This metering or control function is normally defined by one of the following valve types:
a) a shaped plug moving in a linear manner axially within a round orifice or seat ring;
b) a cage with a contoured opening with a linear axially moving piston inside the cage; or
c) a simple on/off quick opening style seat often characterized by a very short stroke.
In each of these examples, the shape is such that the flow passes between the plug/piston and the seat/cage and as the valve stroke (travel) is adjusted, a characterized flow pattern is attempted. The aseptic and pharmaceutical markets have some unique requirements. These needs include inert surfaces, zero unswept geometries and the ability to create an environment that can secure the survivability of possible micro-organisms within the flow stream. To provide fluid stream compatibility, the internal surfaces are normally made of 316/316L stainless steel and are held to very fine finished surfaces. To support the stringent requirements for a clean and sterile environment, there can be no corners, cracks, seams or voids that would allow material from the fluid stream to accumulate and at a later time, contaminate the flow stream. Very fine surface finishes also add to the cleanliness attribute.
And finally, there is a need for micro-organisms in the flow stream to survive the interaction with the control valve. The most detrimental interaction would occur when the plug/piston engages the seat/cage in valve types a) and b) above. While this is absolutely necessary for fluid control it is not good for microbes in the stream. Normally, both of these components are made of metal and when they close, thus stopping flow, the metal to metal contact will literally crush the microbes in the stream, clearly an undesirable occurrence. Design limitations of the valve types a) and b) above do not allow them to meet the standards in the bioprocessing and pharmaceutical markets. These designs do not meet the needs but can provide good control of the fluid stream.
Whereas the valve type ‘c’ designs do meet the design/suitability needs of those markets, their ability to perform as a control valve is very poor. These types of trims are normally referred to as a “Quick Opening” trims.
Their length travel is quite short and due to the non-contoured shapes and lack of interaction between the seat and plug, their use as a capable control valve is minimal. For a process to be valid, whether it is biological, pharmaceutical, chemical, nuclear or any other industry, the valves that control these processes must, without exception, provide a predictable flow. Furthermore, the more characterized the flow, the better suited it is for optimum process control.
The technical problem to resolve is the need for a control valve that meets the design and suitability needs for cleanliness, inertness, and survivability of microbes in the flow stream all while providing flow control that meets the needs of sound, acceptable process control practice and to provide a valve that produces a characteristic that supports these control needs. No current valve product is believed to satisfy these needs.